Many commercial compositions containing moisture curable silylated polymers are known, and have many commercial applications. For example, silylated polyurethane resins are useful as coatings, adhesives, sealants and industrial elastomeric goods.
The curing of these moisture curable silylated polymer compositions requires the use of curing agents. Organotin compounds (e.g. dibutyl tin dilaurate (DBTDL)) have proved to be the most effective compounds to catalyze the curing process which comprises hydrolysis/condensation reactions of the silylated polymers.
However, these organotin compounds are classified as toxic, and therefore, their use should be avoided or limited in articles for human or animal use.
Therefore, there is a need for a tin-free curing agent, which can replace organotin compounds, and which displays at least similar performance levels compared to these compounds.
In the past problems related to the toxicity of tin have been addressed by limiting the quantities of tin in the final polymer, merely reducing the tin level below 0.1 wt %. Alternatively, other organometallic curing agents based on e.g. Zr, Bi, Ti etc. have been screened. Also, pH driven cure processes using amines and/or acids as curing agents have been used for the silylated polymers.
However, these alternatives have not proven to be satisfactory, either the tin levels are still too high from a toxicity point of view or the alternative curing agents do not perform at the same level as tin. Furthermore, some alternative curing agents are known to result in strong discoloring of the polymer, which is not a desired feature.